1. Field of the Invention
The present invention relates to a metal oxide having piezoelectricity. In particular, the present invention relates to a novel piezoelectric material made of a lead-free metal oxide.
2. Description of the Related Art
As piezoelectric ceramics, ABO3-type ceramics such as lead zirconate titanate (hereinafter, referred to as “PZT”) is generally used.
However, PZT contains lead as an A-site element, and hence its effect on the environment is considered as a problem. Therefore, a piezoelectric material using a perovskite-type oxide containing no lead has been proposed.
For example, as a piezoelectric material made of a perovskite-type oxide containing no lead, “Chemistry of Materials” 2006, Vol. 18, No. 21, pp. 4987-4989 describes Bi(Zn0.5Ti0.5)O3 as a Bi-based material. Bi(Zn0.5Ti0.5)O3 is expected to exhibit excellent theoretical piezoelectric performance. However, it is difficult to polarize Bi(Zn0.5Ti0.5)O3 due to a high Curie temperature, and hence the piezoelectric performance thereof has not been clarified.
Further, a piezoelectric material containing BiFeO3 as a main component has been proposed. For example, Japanese Patent Application Laid-Open No. 2007-287739 discloses a BiFeO3-based material containing La in an A-site. BiFeO3 is a satisfactory ferroelectric material, and reportedly exhibits a high remnant polarization amount at a low temperature. However, BiFeO3 has a problem in that the displacement range cannot be kept large under an electric field application due to its low insulation performance.
Further, “Chemistry of Materials” 2007, Vol. 19, No. 26, pp. 6385-6390 discloses a BiAlO3 piezoelectric material obtained by a high-pressure synthesis method. However, the piezoelectricity of BiAlO3 has not reached a practically applicable range yet.
The present invention has been achieved in order to solve the above problems, and an object thereof is to provide a Bi-based piezoelectric material excellent in performance as a piezoelectric material.